Many valve types have been employed for stopping and controlling the flow of fluids in a pipe or other flow path. Each type of valve offers certain advantages and disadvantages. Some valve types include plug valves, ball valves, stop or globe valves, angle valves, butterfly valves, and gate valves.
Ball valves include a rotatable ball having a bore therethrough corresponding to the fluid flow path together with a seat for sealing with the ball surface. Typical ball valves have a valve body and a valve member operatively connected to the valve body by an upstream and a downstream seal. The valve body defines a flow passage having an upstream flow-through end, a downstream flow-through end, and a valve receiving chamber located between the upstream and downstream flow-through ends of the flow passage. The valve member (i.e., the rotatable ball) is located within the valve receiving chamber, and includes a throughbore that allows passage of fluid through the valve member. The seals and seats, in conjunction with the valve member and the valve receiving chamber, define a cavity around the valve member. To prevent leakage of the valve, the seals and seats are pressed against the valve member with a sealing pressure based, at least in part, on the maximum pressure environment in which the valve may be installed. The seals are typically oriented such that the valve member wedges between the seals in the valve receiving chamber: when the valve member is pressed farther into the valve receiving chamber, the pressure on the seals increases.
The valve member may be coupled to an actuator or a handle via a valve stem, which is selectively rotatable to rotate the valve member within the valve receiving chamber, between a fully open position and a fully closed position. Generally, in a two-way valve, the fully open position occurs when the throughbore is aligned with the flow passage at zero degrees of rotation from a centerline of the flow passage and the fully closed position occurs at ninety degrees of rotation of the valve member from the centerline.
It is generally known to adjust the seating of a ball valve without full disassembly of the valve. For example, U.S. Pat. No. 3,058,484 describes a ball valve with wedged seals. To adjust the seating, a packing nut is removed or backed off and the stem is moved upward to engage a splined portion of the stem 44 with an annular sealing member. The annular sealing member is then screwed downward to press the seals into the wedge and to tighten the seals against the ball. The stem is lowered back into engagement with the ball, and the packing nut is retightened for continued operation of the valve.
U.S. Pat. No. 3,132,836 describes a ball valve with converging valve seals that can be urged together and against a ball by tightening an adjusting nut.
Coil or other spring members may be used to automatically bias valve seals against valve balls, including after wear of the ball and/or valve seals, as shown, for example, in U.S. Pat. No. 3,384,337.